Evolution of Two Urbanized Estuaries: Environmental Change, Legal Framework, and Implications for Sea-Level Rise Vulnerability

Abstract

Abstract:The San Francisco Bay (CA, USA) and the Tagus Estuary (Lisbon, Portugal) share striking similarities in terms of morphology and urban development. A finer analysis of development patterns reveals crucial differences in the extent of shoreline alteration and types of land use that now encroach upon natural estuarine habitat. Through historical map analysis and prior stratigraphic and historical research, we reconstruct in GIS environment the evolution of both estuaries over the last millennia and the relative distribution of different classes of land cover. We also discuss the legal frameworks that accompanied this evolution, and how they have influenced the process of wetland reclamation and landfilling. We compared the legal history and synchronous patterns of development by compiling historical mapping information and resorting to GIS analysis to explore spatial patterns over time. This method was useful in isolating events and decisions that were unique to each of the case studies. The Tagus Estuary has experienced disruption of natural environments for over two millennia. Yet, the State has been able to keep estuarine lowlands under public control, even if vast areas have been transformed into farmland. Public control could allow wetland migration with rising seas and restoration efforts. The San Francisco Bay was affected by several decades of elevated sediment loads in the 19th century, which induced rapid wetland expansion, but virtual cutoff of sediment supply by dams in the 20th century now impairs their ability to accrete. Meanwhile, tidal wetlands were subject to extremely fast and poorly regulated development. Artificially filled and/or drained wetlands were transferred to local governments and private landowners, in violation of the Public Trust Doctrine. The transformation of wetlands into salt ponds, industrial zones and even residential neighborhoods created extensive developed areas at or below sea level, which are vulnerable to even modest rises in sea level. Remaining wetlands are now heavily encroached on their landward side by urban development, which prevents their landward migration. Different legal interpretations of comparable definitions of public trusts and jurisdictions over shorelines may have significant implications for the ability to adapt to sea-level rise.

Adapting to sea level rise: Emerging governance issues in the San Francisco Bay Region

“…Local adaptation around the San Francisco Bay has focused on two main types of interventions: 1) the upgrading of existing coastal defense structures, in articulation with evolving United States Army Corps of Engineers (USACE) standards and Federal Emergency Management Agency (FEMA) flood maps; and 2) the restoration of wetlands. The later was perceived as a priority from very early on (Williams 2001), as the impounding, dredging, and landfilling of wetlands for development (Swanson 1975: 85) had reduced the regional provision of tidal wetlands to less than 10% of its early 1800s levels (Goals Project 1999, Williams 2001, Madsen 2007, HDR 2014, Pinto 2016.…”

Evaluating the Functioning Mechanisms of ‘TANK Systems’ in Peri-Urban Areas of Chennai, India—Land Use Change as the Determinant

“…Integration of different types of data has been known to impart clear social understandings and solutions that can provide valuable insights for policy, governance, and management actions [10]. Analysis of spatial patterns over time with the help of GIS [48], in this research, had led to the isolation of events that caused the change in the water management systems. The spatial analysis combining land use maps and data from the survey had imparted clear understanding of the underlying spatial aspects of the land use change.…”

Des mots du politique aux maux du territoire. La performativité des récits métropolitains dans la gouvernance de la nature estuarienne

“…L'urbanisation de ces métropoles estuariennes agit sur les flux démographiques et accentue la concentration des populations dans des espaces dont les vulnérabilités écologiques deviennent de plus en plus évidentes. Ces fragilités résultent d'une combinaison entre leur géomorphologie (Pinto et Kondolf, 2016) et les tracés hydrologiques dessinés par l'urbanisation (Kondolf et Pinto, 2017). Les métropoles estuariennes ainsi que leurs territoires environnants se situent à l'avant-scène de l'exposition à des perturbations environnementales.…”